1. Field of the Invention
The present invention relates to a system for removing spots from a character image. More specifically, the present invention removes noise resulting from optical character recognition in an optical character reader for reading duplicate slips.
In recent years, an optical character reader has been available for reading characters from various kinds of slips. It is, however, essential that an input slip image does not contain spots resulting from stains or erasure residue. As is the case with a slip duplicated by a non-carbon copying paper (that is, a slip including multifarious spots), recognition precision deteriorates.
2. Description of the Related Art
A conventional optical character reader can detect free or liberated spot (resulting from a stain) in a character image and delete the spot while reading a slip. The procedure will be described in conjunction with an explanatory diagram of FIG. 1 showing a prior art. In FIG. 1, a symbol A denotes a character image read by an optical character reader. An image is formed by pixels within a frame range defined by a height (H) and a width (W). The image contains masses of black pixels, A and B. Flags are assigned to the respective black pixels belonging to the large mass A and small mass B, respectively. It is then checked if the flags are connected mutually. As a result, it is recognized that the masses A and B are separated from each other. Thereafter, the number of masses is compared with a value predetermined relative to a type of characters to be read. If the number of blocks exceeds the predetermined value, the smaller one of the separated masses (that is, mass B) is deleted as a spot. Alternatively, character recognition is performed (according to a conventional method such as pattern matching) to see if a character is recognized in the character image including the masses A and B. If no character is recognized in the mass B, the mass B is deleted as a spot.
In recent years, there has been an increasing demand for reading of slips duplicated by non-carbon copying paper. However, duplicate slips are liable to bend or develop a color by a strong touch. The duplicate slips therefore always contain a spot (the spot results from stains or the like, which is the case true for the following description). Thus, an optical character reader has a problem maintaining satisfactory recognition precision due to the spot.
In other words, free spots or spots incidental to a character image by a cut-out or partitioned method can be suppressed to some extent owing to the aforesaid prior art. However, spots in contact with an original character image cannot be deleted.